Effective light sources for projectors may be constructed from lamps with high brightness such as high intensity discharge (HID) lamps, light emitting diodes (LEDs), or lasers. A light source with low etendue can be efficiently coupled through a projector when the etendue of the light source is less than or equal to the etendue of the following optical system in the projector.
Most stereoscopic projection systems can be characterized as one of two basic types: (1) time-sequential projection that uses one spatial light modulator (SLM) per color and alternately shows left eye images and right eye images in rapid sequence, and (2) simultaneous projection that uses two SLMs per color, one for the left eye images and one for the right eye images. In a third type, split image projection, there is only one SLM per color, and the left and right eye images are formed simultaneously on separate parts or pixels of the single SLM.
Stereoscopic left and right images may be formed by using spectral selection, for example as described in U.S. Pat. No. 6,283,597, the complete disclosure of which is incorporated herein by reference. In the spectral selection method, first wavelength bands of red, green, and blue are passed to the left eye, and second wavelength bands of red, green, and blue are passed to the right eye. The first bands and second bands are distinct so that there is little or no overlap between the first and second bands.
The optical designs of most digital image projectors use SLMs to switch each pixel on and off in order to create a visual image. The SLMs may be reflective, such as liquid crystal on silicon (LCOS) devices and digital micromirror devices (DMDs), or may be transmissive such as liquid crystal display (LCD) devices.